The objective of the proposed research is to determine and define those essential characteristics of a molecule which are responsible for its ability to either induce or suppress an immune response. We propose to approach this goal by deliberately and systematically varying the molecular properties of an immunogen and determining the changes in biological response which result. Experimentally, this will be done by creating new classes of simple polymeric molecules of sharply defined chemistry, size and geometry. These will be used as tools for dissecting the immune response into its underlying molecular and cellular components. In a continuation of work previously done, where the in vivo immunological response was measured in mice injected with a series of size fractionated linear polymers of acrylamide substituted with hapten, this project proposes: 1. cell fractionation and culture methods to identify the specific cell types participating in and controlling the response level. 2. Quantitative study of the immune response against highly fractionated polymers in cell culture to test the validity of several alternative models of B-cell activation. 3. Extension of fractionated polymer studies to a wider range of molecular weight and degree of substitution as well as to different haptens and different chemistry of carrier. 4. A study of the molecular characteristics of the immunogen which must be altered to change an immune response from a T-cell independent type to a T-cell dependent type.